Leaf type doors, especially for a bus, are often moved between open and closed positions by a rotatably driven axial shaft joined to the door leaves by link arms to produce a swinging opening and closing movement. Generally, the power source, at the end of the closing movement of the door leaf, produces an axial upward movement of the shaft and leaf. This movement serves to seal the top of door leaf, and may also, through the use of a suitable locking mechanism, serve to lock the door leaves against being accidentally pushed outwardly.
The U.S. patent to Horn, U.S. Pat. No. 4,308,691, shows a vehicle door of the general type described above which incorporates a locking mechanism consisting of a pair of wedge members, one attached to the door frame and one attached to the door leaf. At the end of the door closing cycle, when the shaft is moved upwardly by the driving mechanism, the two wedges frictionally engage to lock the door leaves against any opening movement caused by a push from the inside. There are several drawbacks to such a design. Because of the frictional engagement between the locking members, a friction reducing insert is necessary. This frictional engagement would, of course, tend to retard the upward movement of the shaft and put extra strain on the power source. In addition, any binding therein might interfere with the downward movement of the shaft which could create a problem in opening the doors manually in the event of power source failure. Furthermore, it could be difficult to retro-fit such a locking mechanism into door opening mechanisms for bus body designs involving curved doors and door frames.